Filter cartridges or candle-type filters generally comprise a support structure which is elongated and generally cylindrical and which are provided with a axially extending filter body supported by the structure. The support structure can comprise at least one tube formed with throughgoing opening and closed at its ends by respective end caps.
Filter cartridges of this type can use a wound or pleated filter layer as the filter body and the filter body should be sealingly closed at the two end caps to allow the filter material to be forced through the filter body without escaping around the filter material an without passing between the filter layer and an end cap.
With conventional tubular filter elements, especially filter cartridges, of this type, the tube or tube pair provided between the end caps is not capable of sustaining significant axial yieldability. The central or inner tube of the tube pair can be inserted in corresponding annular grooves formed in the inner phases of the end caps while the support or outer tube has both of its ends fixed to the end caps.
The support structure of conventional tubular filter as filter candles or candle filters because of their shapes, is generally composed of a plastic inert to the material to be filtered, the support structure having a coefficient of expansion or contraction when subjected to the effects of external factors such as changing temperature during filtration or sterilization with steam or the like, which differ from those of the respective filter body.
The filter body or the wound or pleated filter layer can thus be subjected to axial tensile or compressive stress which can cause mechanical damage to the filter. For example the filter layers may show local microcracks which can permit the material to be filtered to break through in an unfiltered manner. Other filter bodies can be damaged in other ways. The problem is most pronounced with sensitive filter layers such as filter membranes.